The process of resin transfer molding typically comprises injecting a precatalyzed resin into a closed mold. Once the mold is filled, the resin is cured and the part ejected. Often, the resin is injected through a dry fiber preform preplaced in the mold for enhanced structural integrity.
In order to achieve high volume production, a heated mold is used to shorten overall cycle time by reducing the filling and cure times of the process. However, prior art shell molds have poor thermal response characteristics due to their high thermal mass, and therefore are unable to operate at high processing temperatures and unable to dissipate heat effectively.
As the resin cures within the mold, a significant amount of heat is given off by the resin (this release of heat is termed "exotherm"). If the exotherm heat is too high, the resin may crack due to excessive shrinkage, or other material defects such as surface imperfections, discoloration, or poor dimensional control may occur. Accordingly, when exotherm heat is high, the normal processing temperature of the mold must be maintained at a low level in order to avoid such resin problems.
It is desirable to process the resins through a mold at higher temperatures and to provide means for dissipating the exotherm heat to prevent damage to the resin while allowing such processing at higher temperatures. Prior art RTM shell molds are typically solid, heavy objects with a heavy concrete support structure, or other solid structure. Such prior art molds are not thermally responsive enough to provide exotherm heat dissipation to allow higher processing temperatures.
A thermally responsive mold would not only permit higher processing temperatures, but would also allow the use of high reactivity resins, thus resulting in greater in-mold cure, better dimensional control, shorter cycle time, and fewer component defects due to resin cracking from excessive shrinkage, surface imperfections or discoloration.